Electrolytic production of titanium tetrahalides



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United States Patent-O ELECTROLYTIC PRODUCTION OF TITANIUM TETRAHALIDES Walter Judo, Lexington, and Mary C. Cretella, Lawrence, Mass., assignors to Ionics, Incorporated, Cambridge, Mass., a corporation of Massachusetts Application October 30, 1953, Serial No. 389,284

' 12' Claims. Cl. 204-61) This invention relates generally to method and apparatus for the production of titanium tetrahalides from titaniferous ores, slags or concentrates; and more particularly, to the electrolytic preparation of tetrahalides,

has increased rapidly to the point where large scale uses are contemplated. Present practical methods for preparing the metal in a useful state use the tetrahalides as the ultimate reactant. These materials do not exist in nature and it has become increasingly obvious that the'high-grade titanium ores, the primary starting ma terials, are not available in suflicient quantity to permit the production of low cost metal. However, very large quantities of combined titanium are found in low grade ores usually with considerable amounts of compounds of iron, calcium, magnesium, and silica. The titanium content may be concentrated by appropriate treatment or may be left in the slag from well known processes for recovering the iron content. Methods have been sought for the preparation of titanium tetrahalides from these materials.

This invention is directed to a more eificient, economical, and controlled method for preparing titanium halides than those previously known wherein the products of the process are obtained in substantially pure form suitall able, for example, for use in the production of titanium I metal by well known processes. This method employs an electrolytic cell of such types known as'the Downs or Knapsack cells or U form containing a fused metal halide, in which the submerged anode of the cell comprises titanium-bearing material prepared by the high temperature reaction of titaniferous ores, slags and concentrates with carbonaceous reducing agents or mixtures of titaniferous ores, slags and concentrates with nonvolatile carbonaceous reducing agents. When a direct electric current is passed therethrough, halide ions travel 1 are formed. Furthermore, any iron halides which may be formed from contaminants in the titanium-bearing anode would volatilize only slightly with the titanium halides owing to the low vapor pressure of iron halides In such a process, the in coal in the ratio of 0.2 part to 0.7 by weight 2,870,071 Patented Jan. 20, 1959 v 2 above mixed melts of alkali or alkaline earth halides and iron halides. Accordingly, the iron halides formed dissolve in the fused salt electrolytic bath and in the absence of preventative measures eventually cause depo sition of metallic iron in the cathode section. Iron does not alloy appreciably with alkali or alkaline earth metals, and falls to the bottom of the cathode compartment where it may be recovered. It should be noted that titanium tetrahalides are substantially insoluble in the fused salt electrolyte, and accordingly volatilize without substantial loss from the fused salt bath.

Accordingly, it will be apparent that by the practice of this invention, the deleterious effects of metal contaminants in titanium source materials are overcome and a high purity titanium halide product is obtained in a most etlicacious manner whereupon pure titanium metal may be subsequently obtained in processes well'known, per se; for example, by reduction with the elemental alkali or alkaline earth metals formed at the cathode.

The fused electrolyte bath of this invention comprises the halides of alkali or alkaline earth metals and mixtures thereof. When mixtures of alkali and alkaline earth halides are employed for the electrolyte bath, such mixtures may be of eutectic character to permit comparatively low electrolyte temperatures. It should be noted that the elemental alkali or alkaline earth metal formed at the cathode in carrying out the method of the invention is of the sort required in known processes for producing elemental titanium from titanium tetrahalides, T his feature is an important aspect of the invention. The select on of the composition of the electrolyte bath deg pends upon the desired products of the electrolysis. For example, if titanium tetrachloride is desired, chloride salts must be used. If Na or Mg metal is desired, the

halide selected would be the Na or Mg salt, respectively. A

The high temperatures necessary to maintain the electrolyte in a fused state may be obtained by external heating, although heat is contributed by the passage of current through the electrolyte. The temperatures employed in the fused bath are of the order of MiG-98090., depending upon the composition of the salt bath. At these temperatures satisfactorily high yields are obtained, local solidification is avoided and corrosion of construction material is minimized.

One of the important features of the present invention is the use of a titanium carbide containing material (possibly also containing substantial quantities of titanium monoxide, nitride and/or carbonitride) as the anode of the electrolytic cell to be described hereinafter. It is not necessary that such titanium compound be pure; for example, material containing mixtures of titanium carbide and. titanium monoxide may be used. The latter mixtures, however, are often referred to as titanium carbides, and are considered to be solid solutions of titanium monoxide and titanium carbide with a crystal structure similar to that of titanium carbide. Such mixtures of titanium monoxide and titanium carbide (possibly containing titanium carbonitride and nitride) may be eftectively produced by the carbonaceous reduction of ii taniferousores such as ilmenite and rutile, and slags therefrom, above 1400" C. The amount of titanium monoxide in the product may be controlled within limits by regulating the weight ratio of carbon to ore in the carbonaceous reduction charge. Alternatively the an odes may be fabricated from an intimate mixture of pulverized titaniferous ores, slag or concentrate and a non volatile carbonaceous reducing agent such as coke or of reducing agent to the titanium source material. i

The reaction of the titaniferous material with the carbonaceous reducing agent is carried out at a temperature between 1300 and 1500 'C. or higher, and preferably at or above the melting point of the titaniferous material. Suitable carbonaceous reducing agents are coal, graphite, coke, charcoal, petroleum oils, residual fuel oil, methane, ethane, and other hydrocarbon gases such as coal gas, mixtures of hydrocarbons, or even hydrogen, etc. The titaniferous materials are preferably ground or otherwise comminuted to pass 40 mesh sieve and are mixed with the carbonaceous reducing agent as a liquid, solid or gas, and then heated in an induction, are, resistance, or other furnace at the temperature indicated above. In the event that a gaseous or volatile carbonaceous reducing agent is used, the comminuted titanium source material may be first preheated to the reactionv temperature and the reduc ing material passed into the heated mass.

During the course of the reaction betweenv the titanium source material and the reducing agent, considerable quantities of carbon monoxide will be evolved and the commencement and termination of the reaction may be followed by the initiation or cessation of this evolution.

The resulting mass, presumably containing lower oxides of titanium as well as impure titanium carbide, is cooled and then comminuted by well-known means, per se, and pulverized to a desired particle size. Preferable particle sizes are in the range of 40-300 mesh.

it has been found that electrodes are-preferably prepared from such materials in the pulverized state by mixing the same with a binder, molding, and baking at temperatures of about 300-400 C. or higher. The binder material may be, for example, carbohydrates such as molasses or dextrose although tar or pitch binders are also suitable. The titanium bearing anode material may be given the shape of rods, bars or other forms suitable for complete or partial submersion in the fused electrolyte and for ready replacement upon depletion of the charge.

Figure l diagrammatically illustrates a suitable apparatus for conducting the process in accordance with the invention.

Figure 2 diagrammatically illustrates a modified form of apparatus for carrying out the process of this invention.

The apparatus of Figure 1 comprises a fused salt cell, the body of which is a U-tube which is held in vertical position with the bend of the U at the bottom. External heat is supplied to the cell by mounting the U-tube in an electrical resistance furnace, the latter being provided with appropriate insulation such as refractory cement with an outside coating of magnesium carbonate, asbestos, etc. One vertical arm of the U-tube serves as the cathode compartment, the other, the anode compartment. Both arms are closed to prevent air attack on the electrode products. A side arm sealed to the upper portion of the anode arm of the U allows gaseous reaction products (substantially pure titanium halides) to escape from the anode compartment. A similar side arm at the cathode compartment is used to control the gas pressure at the cathode and thus keep the level of the molten salt constant in both arms. A condenser is connected to the side arm of the anode compartment to condense the gaseous product. Vent lines from the cathode and anode sections of the cell are equipped with gas driers such as drying tubes with anhydrous calcium chloride or Dry Ice traps, in order to prevent any possible contamination of the cell contents or products with water vapor. Further precautions against the reaction of water vapor may, for example, consist of flowing an inert gas such as argon, helium, methane, nitrogen, etc. through both anode and cathode compartments, thus providing a positive pressure within the cell. The anode and cathode leads are nickel, platinum, or other suitable material inserted through the plugs at thetop'of the compartments providing electrical connections to a l). C. power source. The cathode lead connects to a suitable electrode (preferably of nickel) which is submerged in the, molten salt. The anode lead is electrically connected to the TiC anode; for example, by passing through a hole in the TiC anode, or by being. imbedded in the anode material. It is not always necessary to attach the TiC material to the Ni anode wire. All that is necessary is that contact between the same should be made; for example, such a contact could be effected by compressing the TiC material against the Ni wire. The TiC anode is partially or wholly submerged in the molten salt, and the D. C. circuit is completed from anode to cathode by conductance through the molten salt, The temperature of the electrolytic cell may be conveniently measured with a Chromel-Alumel thermocouple attached to the outside of the U-tube.

In operation, the cell is filled with a sutficient amount of a dry halide salt, or salt mixture, so that the level of the molten salt in the cell will rise above the top of the U bend and bathes the electrodes thus preventing electrode products formed in one arm from mixing with those in the other. The temperature of the electrolyte is then raised to the range of 400 to 990 C. and preferably about 660 C. by the heating in the resistance furnace. After the desired temperature has been reached, the anode and cathode are inserted in the molten salt whereupon an inert gas, such as argon, is passed through both electrode compartments. The pressure of the inert gas is regulated to maintain an equal level of molten salt in both arms of the U-tube. Direct current is then passed through the system whereupon a vigorous evolution of titanium tetrahalide in the anode compartment results. The titanium tetrahalide vapor passes through the anode sidearm and liquifies in the condensing chamber of the anode section. The metal of the fused electrolyte forms an elemental layer at the surface of the electrolyte in the cathode compartment.

The apparatus of Figure 2 comprises a current-conducting crucible which acts as the cathode of the cell as well as the container for the fused salt. Positioned vertically therein is a combination diaphragm and distilling head, the lower portion of which is perforated to form the diaphragm separating the anolyte from the catholyte. The head is provided with a cover cemented thereto with alundum. Vents are provided in the cover for flushing the apparatus with an inert gas to prevent or moisture contamination with the products of the reaction. The top of the head is provided with a cap through which passes a porcelain insulator. The partially submerged TiC anode is supported by a conducting wire which passes through the porcelain insulator. At the upper section of the head an open side arm is provided through which the volatilized Ti tetrahalide passes to a cold trap (not shown). Just above the crucible cover a side arm is pro vided to allow flushing the head with dry inert gas. The crucible is enclosed in an electric resistance furnace as clearly shown in the drawing (Figure 2). The operation of this electrolytic cell in the production of Ti tetrachloride is fully set forth in Example 4, hereinbelow.

While the present disclosure and examples below describe more particularly the electrolytic production of titanium tetrahalide, it should be understood that the present invention is not so restricted since other metal halides such as Si can also be prepared according to this invention.

The following examples will show how the improved methods of this invention are used in the production of titanium tetrachloride and tetraiodide.

Example 1 (apparatus of Figure 1) Titanium carbide anodes were made by mixing ten parts by weight of titanium carbide with one part by weight of dextrose. Snfficient water was added to bring the whole to a liquid state. The mixture was then heated until it thickened to a sticky syrup. Upon cooling, the resulting viscous mass was rolled into rods which was then further heated in a furnace to 520 C. under an inert atmosphere of argon for about four hours. This rod was broken into appropriate anode rods.

A titanium carbide anode weighing 4.2 gms, 0.7 cm. in diameter and 3.1 cm. long, was suspended on a' nickel wire in the anode compartment of a fused salt electrolysis Example 2 (apparatus of Figure 1) In this run the fused salt bath consisted of an eutectic mixture of 59 mol percent LiCl and 41 mol percent KCl with a melting point of 352 C. The electrolytic cell was brought to and maintained at temperatures between 403 to 437 C. by means of an electrical resistance furnace made of a core of alundum upon which a heating coil of Nichrome wire was wound and covered by refractory cement. The cathode consisted of a nickel wire which was sealed into the top of the cathode arm of the U-tube and'extended into the molten bath. The anode consisted of a TiC cylinder obtained from the batch described above and had a total surface area of- 1.8 square cm. Into the other arm of the U-tube, anothernickel wire was attached to the TiC cylinder, which in turn was immersed in the salt bath. The amperage of the cell was maintained between 1 and 1.7 amps. throughout the run, which gave an average current density of 0.3 to 0.4 amp/cm. The voltage of the cell varied from 9.7 to 11.6 volts.

A stream of argon was maintained in each of the side arms of the U-tube. In the anode arm this not only provided an inert atmosphere for the TiCL; produced, but also was a means of carrying the gaseous product to an attached cold trap which condensed the tetrachloride gas to liquid. The argon then passed through a KOH trap which removed any TiCl which may not have been condensed out before venting to the atmosphere. The argon introduced to the cathode arm was used solely for maintaining a balance of pressure and an inert atmosphere for the molten metal collected there.

A total product of 1.28 gms. of TiCL, was collected during a 11111 of 48 minutes; 0.89 gm. in the cold trap and 0.39 gm. in the KOH trap. The yield in this run was 72.9%.

as'rop rr nace.

lyte. The head was provided with a close fitting alumina cover cemented to the head with an alundumcement. The cover was carefully positioned to prevent the bottom of the'head from contacting the base'of the nickel crucible. Vents were provided in the cover (sealed with alundum cement) to provide flushing at a slight positive pressure with argon gas to prevent contamination of the products with air and moisture. The vertical portion of the distilling head was wrapped above the alumina cover with asbestos tape. The top of the headwas provided with a stainless steel cap through which passed a porce-.

lain insulator. The TiC anode was supported by nickel wire (imbedded therein) which passed through the porcelain insulator. A tapered stainless steel joint was pro vided at the end of the uppermost side arm to fit a standard ground glass joint connecting to a cold trap as previously described. Just above the alumina cover a side arm was provided to allow flushing the head with dry argon gas, which flow was maintained throughout the run. The nickel crucible was heated in an electric resistance fur- The anode was composed of a mixture of a pulverized titanium-bearing slag known as Sorel slag having a composition of 69.9%of Tl02, 9.9% FeO, 0.4% Fe, 0.6% U 0 0.9% CaO, 6.3% SiO and minor other impurities (resulting from the iron smelting of a low-grade titanium ore) mixed with 0.7 part by weight of conducting graphite powder, the whole being bonded with molasses and baked around the nickel wire in a cylindrical mold at 500 C. The anode was about ,5 inch in diameter and about 2 inches in length. The electrolyte was a mixture of 56 mol percent anhydrous NaCl and 44 mol percent anhydrous MgCl The temperature of the melt was maintained in a range of 550-600" C. The anode was immersed in the melt to somewhat over half its length so that somewhat more than 1 inch was immersed at the beginning of the experiment. A direct current was maintained at 7 amps. for 20 minutes at a voltage varying between 6 and 9 volts. The metal collected in the cathode compartment was substantially pure Mg. Approximately 4.4 grams of high quality TiCl were collected, amounting to about 75% current efiiciency.

In a series of similar runs using anodes of the same composition as Example 1, and the apparatus of Figure 2,

5 the following results were obtained:

Electrolyte, Current, Duration, Yield, Percent Example M01 Percent Temp., O. Amperes Minutes Grams A 30% NaC1-- C 500 to 550.... 3.5 40 3. 2 78 e {2% $29 1: }600 to 2. s so a. a 12 Example 3 (apparatus of Figure 1) In a similar run as noted in Example 2 and where the fused bath consisted of NaI, the anode being of the same titanium carbide material, the temperature of the fused bath being maintained between 650-820 C., the current 3 to 4.7 amps, the voltage 11 and the time of operation 29 minutes, 4.6 grams of Til was obtained, which represented a 48% yield.

Example 4 (Figure 2) Having thus disclosed our invention and described in detail preferred embodiments thereof, we claim and desire to secure by Letters Patent:

1. In the method of producing titanium tetrahalides of the group consisting of chlorides, bromides and iodides, the steps of electrolyzing a fused bath of separated anode and cathode compartments of the salts of the group consisting of the alkali halides, alkaline earth halides, and mixtures thereof, said halides comprising the group consisting of chlorides, bromides, and iodides, using as the anode electrode compacted pulverized titanium carbide containing material, said anode electrode being at least partially submerged in said fused salt bath thereby causing gaseous titanium tetrahalides to form at the anode and at the same time the pure metal of said halides at the cathode, and collecting and condensing the vapors of said titanium tetrahalides from the upper portion of said anode compartment. 1

2. The method of claim 1 wherein the halide is a chloride.

3. The method of claim 1 wherein the fused bath con- 'sists of NaCl.

4. The method of claim 1 wherein the fused bath consists of MgCl;;.

5. The method of claim 1 wherein the halide is an iodide.

6. The method of claim 1 wherein the fused bath consists of Neil.

7. The method of claim 1 wherein the fused bath consists of an eutectic mixture of LiCl and KCl.

8. The method of claim 1 wherein the fused bath consists of an eutectic mixture of NaCl and CaCl:.

9. The method of claim 1 wherein the fused bath consists of an eutectic mixture of NaCl, KCl, and MgCl 10. The method of claim 1 wherein the fused bath is maintained at temperatures between 400900 C.

11. The method of claim 1 wherein the temperature of the fused bath is maintained at a temperature of about 600 C.

12. The method of producing TiCL; in an electrolytic cell which comprises electrolyzing a fused NaCl bath wherein the anode of the electrolytic cell is composed of a TiC containing material submerged in said fused bath,

separating the volatilized TiCl at the anode compare ment and recovering the pure Na metal at the cathode compartment.

References Cited in the file of this patent UNITED STATES PATENTS 1,343,662 Danckwardt June 15, r1920 2,636,856 Suggs et al. Apr. 28, 1953 2,712,523 Alpert et al. July 5, 1955 2,722,509 Wainer Nov. 1, 1955 FOREIGN PATENTS 334,475 Germany Mai. 14, 1921 452,269 Great Britain Aug. 19, 1936 679,419 Great Britain Sept. 17, 1 952 137,626 Sweden Oct. 14, 1952 1,087,091

France Aug. 18, 1954 OTHER REFERENCES Hackhs Chemical Dictionary, 3rd edition, published in 1950, page 771.

Mellor: Comprehensive Treatise on Inorganic Chem, vol. 7 (1927), pages 78 and 79.

Notice of Adverse Deeisien in interference In Into iorenoe No. 92,286 involving Patent No. 2,87 0,071, W. Judo and M. G. 'Cretella, Electrolytic production of titanium tebmhalides, final judgment adverse to the patentees was rendered Aug. 19, 1964:, as to claims 1, 2, 3, 4, 5, 6,7, 8, 9, 10 and12.

[Ofiioial Gazette January 19, 1965.] 

1. IN THE METHOD OF PRODUCING TITANIUM TETRAHALIDES OF THE GROUP CONSISTING OF CHLORIDES, BROMIDES AND IODIDES, THE STEPS OF ELECTROLYZING A FUSED BATH OF SEPARATED ANODE AND CATHODE COMPARTMENTS OF THE SALTS OF THE GROUP CONSISTING OF THE ALKALI HALIDES, ALKALINE EARTH HALIDES, AND MIXTURES THEREOF, SAID HALIDES COMPRISING THE GROUP CONSISTING OF CHLORIDES, BROMIDES, AND IODIDES, USING AS THE ANODE ELECTRODE COMPACTED PULVERIZED TITANIUM CARBIDE CONTAINING MATERIAL, SAID ANODE ELECTRODE BEING AT LEAST PARTIALLY SUBMERGED IN SAID FUSED SALT BATH THEREBY CAUSING GASEOUS TITANIUM TETRAHALIDES TO FORM AT THE ANODE AND AT THE SAME TIME THE PURE METAL OF SAID HALIDES AT THE CATHODE, AND COLLECTING AND CONDENSING THE VAPORS OF SAID TITANIUM TETRAHALIDES FROM THE UPPER PORTION OF SAID ANODE COMPARTMENT. 